tlandwehr asked about a rental car company that offers unlimited mileage and no geographic restrictions, which is different from one-way rentals.

I have heard that Hertz may not have restrictions, and I've been told others may waive case by case if you ask them.

This is a frustrating process with car rental companies and has led to many complaints. Althoug I can see the company's point of view, they've made a mess of it and so it seems to be a hidden charge. Most have a clause that kicks in $/mile if you go into an unallowed state, e.g., renting from St. Louis, you can drive in Missouri and surrounding states, but if you go in to Colorado (and they can tell because of GPS tracking now), you broke your unlimited-mileage agreement and $/mile (for the entire trip!) kicks in. So you really need to ask before you sign.

If you go through Hotwire, Priceline, or some other travel dot com, you may find that they exclude that restriction. I called Enterprise to see why, and the rep told me that a contract with a travel dot com might be such that the unlimited-mileage clause is waived. If you don't see it on the dot com, but sign the location's contract and it's in black and white, who do you go to for "arbitration"?

You need to check with the location you are planning to use; however, if you're not sure which location you are going to use because you are trying to find the cheapest deal, good luck!

Bottom line: If you don't want to be surprised by additional charges, look at the rules, and before you actually hit the book button, you may want to call the location.